Field guide training: Arthro­pods – Part 2

Insects are the most successful group of arthropods, evolutionary speaking. More than 60% of all discovered animal species on earth are insects, that means about 1,000,000 single species. They can be found in almost every habitat and are not frightened of hostile environments. The diversity of this group can be divided in 29 subgroups which again split into several families and species.

All insects have three body parts (head, thorax, abdomen) as well as three pairs of legs which are attached to the thorax. Also bound to the thorax are typically two sets of wings of which one is often so little developed that it almost not visible. Some species have lost their wings completely through evolution so that only vestiges remain.

Most insects are equipped with compound eyes which are highly sensitive and allow a high-resolution stereoscopic vision which is not known among any other animal species. To support the sensory perception insects are also equipped with a pair of antennas situated on their heads. The mouthpiece (insect mandibles) can be found outside of the mouth and are used for breaking and ingestion of food.

Insects generally reproduce via sexual reproduction. Their offspring is laid in form of eggs and grows in different development stages depending on the species (egg, cocoon, adult insect). This process is also called metamorphose. It is possible to differ between insect species by looking at their metamorphose behaviours:

• Ametabolous insects: The development takes place without metamorphose which means that juveniles only differ from imagos (adult insects) in their stage of sexual maturity. An example for ametabolous insects is the springtail.

• Hemimetabolous insects: No pupation takes place. The nymph is going through several ecdysis processes while transforming into an imago. Hemimetabolous insects are for example crickets or beetles.

• Holometabolous insects: A complete metamorphose including four stages: Egg, larva, pupa and imago. Two examples for holometabolous insects are butterflies and dragonflies.

Why are insects such a successful group? One reason is most likely their ability to fly. This enables them to populate a wide area and to flee from their predators. Some species have adapted perfectly to their method of transportation and mastered the art of flying. By the way: A honeybee can come up to 190 wing beats per second, while a mosquito can reach up to 1000!

Furthermore, their variety of species, appearances and development stages attracts a wide range of predators. This mean that there is less competition between the different species or the different development stages within one species.

Another reason is the social structure of insects: Especially insect species which appear in colonies or swarms are more powerful due to their high numbers.

The importance of insects within the ecosystem is huge, not only because they function as a main source for food for many other animal species. Insects are also the main pollinator for plants. Over 60% of our crop is dependent on insects such as honeybees and bumblebees. Insects also count as vectors for animal and plant diseases which plays a highly important role in the regulation of populations. Last but not least, insects are a fundamental part of every terrestrial ecosystem because they are responsible for the decompensation of dead biomass (e.g. carcasses) and for bringing it back into the cycle of materials of nature.

By joining one of our courses you have the chance to learn more about the different insect species, their behavior and about their protection